Acquisition Acquisition, Textuals (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Acquisitions [Abstract]
Acquisition Spend	$ 76.2	$ 72.9	$ 68.9
Payments for (Proceeds from) Delayed Tax Exempt Exchange	$ 26.0	$ 3.7	$ 27.7

Net cash outflow or inflow from a property which is traded for the promise to provide a replacement like-kind property in the near future also known as tax deferred exempt exchange.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3179-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3213-108585

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration